Fine structure in the alpha-decay, of the neutron - deficient 191 Po and 191 Bi isotopes

The α-decay properties of the neutron-deficient 191Po and 191Bi nuclei have been investigated at the RITU gas-filled separator using the 5n and p4n evaporation channels of the 36Ar + 160Dy → 196Po* reaction. In contrast to previous studies two α-decaying isomeric states were observed in the decay of 191Po. Evidence was found for α-decay to excited levels in the 187Pb daughter nucleus. The tentative interpretation of these levels could be a weak coupling of the odd neutron to an intruder 2p-2h deformed 0+ state in the even-even core. The difference in the reduced α widths of the α transitions towards the ground state and excited state points to a deformed 13/2+ isomeric state in 191Po. Branching ratios of bα(187mPb)=12(2)% and bα(187gPb)=7(2)% have been experimentally measured. For 191Bi two new alpha-lines have been observed. A more precise half life value of T1/2 = 115(10) ms was determined for 190mBi. (author)